Although conventional thermosetting plastics, such as phenol, epoxide and unsaturated polyester resins used for making duromer molded components may show substantial stability and long-lasting, high-temperature resistance at temperatures up to more than 200.degree. C., these advantageous properties may be limited due to brittleness, particularly at temperatures below 0.degree. C.
Recently discovered latently reactive pasty polyurea systems, can be processed into molded components that demonstrate excellent durability at high and low temperatures. (unpublished German Patent Application P 39 40 159.6). This pasty polyurea system which becomes reactive above room temperature, comprises a masterbatch that includes a methylene diphenyldiisocyanate, which is liquid at room temperature; an alkali halogen salt complex, which is reactive only above 120.degree. C., and 4,4' diphenyl methanediamine or optionally of hexamethylene-6,6' diaminecarbamate, as well as, about 1 to 625 parts by weight (per 100 parts methylene diphenyldiisocyanate) of low-molecular weight, isocyanate-terminated polyesterpolyol-diisocyanate-prepolymer, prepared from polycaprolactone polyol and an isomeric mixture of toluenediisocyanate. This masterbatch, which may have an NCO- excess of up to 15% over the equivalent number of free OH-- and NH.sub.2 -- components, can be strengthened with fillers and is moldable at low pressures. This masterbatch is also useful as an impregnating agent for moldable glass-fiber mats.
Difficulties may arise in the processing the above-described pasty polyurea systems, particularly with molded components having large-surface areas and/or complicated contours, because at processing temperatures more than about 160.degree. C., these highly reactive systems immediately form a polyurea film at points of contact with hot mold cavities which may hinder complete removal of air trapped in the cavity. Another disadvantage of the pasty polyurea systems is that the required diamine complex is commercially available only in combination with a softening agent. The softening agent reduces internal bonding and stability of finished molded components and also reduces the effectiveness of reinforcing additives. Detrimental exudation of the softening agent from such molded components has also been observed.
Although prior art polyurethane duromers comprising highly cross-linked polyurethane aggregates having linear, short chain polyester disocyanate segments could be reacted at higher temperatures than their liquid or liquefied starting components during casting processes; due to the very high reaction rate of such systems, it would be difficult, if not impossible, to control their reaction during actual production.